Classical methods for parameter estimation, including delay and channel estimation in data receivers, such as those used in Global System for Mobile (GSM) terminals typically rely on correlating a received signal burst such as a normal burst, a synchronization burst or the like with a known pattern in the received sequence. In the GSM protocols this known pattern or sequence is often referred to as a midamble or Training Sequence (TS) that is embedded in the central portion of the burst.
Advances in Digital Signal Processors (DSPs) and processing have enabled more extensive and complex calculations that have led to additional techniques to improve channel estimation and other relatively complex signal/data conversions. However DSPs are still limited in performance and these additional capabilities come at the cost of battery life and thermal management issues for increasingly smaller and more complex packages such as portable communications equipment.
At the same time system designers are increasing system capacities or bandwidths and using more complex modulation techniques and communications protocols that dramatically increase processing loads on a DSP or other processing resources. For example, Gaussian Minimum Shift Keying (GMSK) modulation, frequency hopping, significantly higher symbol rates, and increased fixed network transmitter densities are all planned for systems, such as GSM systems. These techniques often result in more rapidly changing channels and in increased levels of interference or noise and, often, increased sensitivities to such channel changes or interference.
Thus noise or interference remain a primary problem facing signal recovery in a receiver. Besides the obvious, common sources of noise or interference are adjacent channel signals or co-channel signals from neighboring transmitters, each capable of generating energy that falls on-channel or may be referred to as on-channel interference. Thus a need exists for improved, preferably less computationally complex techniques for estimating channel parameters. Various modulation methods and systems exist that can benefit from such techniques and advances.